The present invention relates to a biodegradable polymeric composition containing a block copolymer having a hydrophilic poly(alkylene glycol) component and a hydrophobic biodegradable polymer component suspended in a poly(ethylene glycol) medium, and to a method for the preparation thereof. The composition can effectively solubilize a hydrophobic drug and forms a solution which can be stored as a stable liquid formulation. Furthermore, the composition can be injected into the body undiluted or as a diluted solution in an aqueous medium, and therefore is useful for the intravenous administration of poorly water soluble drugs.
Many important drugs are hydrophobic and have limited solubility in water. In order to attain the expected therapeutic effect from such drugs, it is usually required that a solubilized form of the drug be administered to a patient. Therefore, solubilization of a poorly water soluble drug is key technology in the preparation of a formulation for oral or parenteral, especially intravenous, administration of the drug. Common methods used for solubilization of poorly water soluble drugs are: i) dissolving the drug in a co-solvent of a water-miscible organic solvent and water; ii) modifying the drug as a salt that can be soluble in water; iii) forming a soluble drug-complex using a complexing agent; and iv) micellizing the drug in an aqueous medium with a surfactant. (Leon Lachman, xe2x80x9cThe Theory and Practice of Industrial Pharmacyxe2x80x9d, Lea and Febiger, Philadelphia, 1986).
Solubilization methods using surfactants without requiring any changes in the chemical structure of a drug has been widely used to solubilize various drugs. Non-ionic surfactants, eg. polyoxyethylene sorbitan fatty acid esters(Tween(copyright)) and polyoxyethylene alkyl ethers(Brij(trademark) or Myrj(trademark)), are commonly used as the surface active agents. European Patent EP 0645145 discloses a method of solubilizing a typical poorly water soluble drug, paclitaxel, by use of Cremophor EL(trademark), a polyoxyethylene castor oil derivative. The use of these surfactants, however, is restricted due to their toxic side effects such as hypersensitivity, and they have limitations in that their poor ability to stabilize micelles can cause precipitation of the drug when the micellar solution is either stored or is to remain in place for an extended period of time.
Other solubilization methods using a polymeric micelle, wherein the polymer is a diblock or triblock copolymer consisting of a hydrophilic poly(alkylene glycol) derivative and a hydrophobic biodegradable aliphatic polyester or poly(amino acid), has been developed (see U.S. Pat. Nos. 5,449,513 and 5,429,826). However, poly(amino acid) derivatives or other crosslinked polymers used in the formation of polymeric micelles, cannot be hydrolyzed or degraded in the body, which can cause undesired immune reactions.
X. Zhang et al. reported that a polymeric micelle prepared with a diblock copolymer of poly(lactic acid) and monomethoxy poly(ethylene glycol) was useful as a carrier of paclitaxel. (X. Zhang et al., Int. J. Pharm. 132(1996) 195-206), and Shin et al. disclose a solubilization method for indomethacin using a diblock copolymer of poly(ethylene glycol) and polycaprolactone(I. Gyun Shin et al., J. Contr. Rel., 51(1998) 13-22). In these methods, a poorly water soluble drug is incorporated in a polymeric micelle, wherein the polymers are biocompatible and biodegradable. According to their methods, a drug and a block copolymer are dissolved together in an organic solvent, especially in a water-miscible organic solvent such as tetrahydrofuran or dimethyl formamide. The polymeric micelles are prepared by dialyzing the solution in water first and then freeze-drying the aqueous micellar solution. Alternatively, a solution of a polymer and drug in a water-miscible organic solvent, acetonitrile, is prepared. The organic solvent is slowly evaporated to give a homogeneous drug-polymer matrix and the matrix is then dispersed in an aqueous medium at ca. 60xc2x0 C. to form the polymeric micelles.
As described above, a conventional solubilizing method for a poorly water soluble drug using polymeric micelles employs complicated steps including formation of an aqueous polymeric micellar solution containing a poorly water soluble drug, followed by preparation of a freeze-dried powder. Moreover, the powdered product must then be reconstituted when used in a hospital or other setting and it is not possible to store the product in an aqueous solution because of the hydrolyzable and biodegradable component in the polymer. Another disadvantage is that this method cannot be applied to a polymer having a melting temperature below about 50xc2x0 C.
The present invention provides a composition capable of forming a micelle in body fluids or in an aqueous medium and that can be injected into the body in neat or undiluted form or in diluted form as an aqueous solution. The present invention also provides a composition capable of solubilizing a poorly water soluble drug and a method for the preparation thereof.
The composition of the present invention comprises a block copolymer of a hydrophilic poly(alkylene glycol) block and a hydrophobic biodegradable polymer block dispersed or suspended in a poly(ethylene glycol) matrix or its derivatives. The term poly(ethylene glycol) or PEG, as used herein, shall also be deemed to include derivatives of PEG unless otherwise specifically stated. Such derivatives will be more specifically described in the disclosure that follows. Since only the hydrophilic component block, not the hydrophobic component block, of the copolymer has an affinity or attraction for the poly(ethylene glycol) matrix, the block copolymer forms a core-shell structure wherein the hydrophobic biodegradable polymer block occupies the inner core and the hydrophilic poly(alkylene glycol) block forms the outer shell in the poly(ethylene glycol) medium.
Preferably, the block copolymer content in the composition of the invention is within the range of 5xcx9c95 wt %, and more preferably within the range of 10xcx9c50 wt %, and the content of the water soluble poly(ethylene glycol) is within the range of 5xcx9c95 wt %, and more preferably 50xcx9c90 wt %. In a composition containing a poorly water soluble drug, the drug content is preferably within the range of 0.1xcx9c50 wt %, and more preferably 5xcx9c30 wt % based on the weight of the block copolymer.
A biocompatible water-miscible organic solvent may be added into the composition of the present invention to facilitate better solubility of a drug. The added amount of the organic solvent depends on the solubility of a drug, and preferred content of the solvent is less than 50 wt % based on the amount of poly(ethylene glycol) or its derivatives. The present invention is described in detail hereinafter.
The present invention is directed to a composition containing an amphiphilic block copolymer having a hydrophilic poly(alkylene glycol) component and a hydrophobic biodegradable polymer component dispersed or suspended in a poly(ethylene glycol) medium, and to a method for the preparation thereof.
The combined block copolymer and poly(ethylene glycol) composition is a liquid that is shelf stable over extended periods of time. The block copolymer portion of such compositions have a core-shell structure in the poly(ethylene glycol) medium wherein the hydrophobic biodegradable polymer block occupies the inner core and the hydrophilic poly(alkylene glycol) block forms the outer shell in the water soluble poly(ethylene glycol) matrix or medium. When administered, the poly(ethylene glycol) functions as a dispersant to facilitate water solubility and the block copolymer portion of the composition forms a micelle structure in body fluids or in an aqueous medium. When a drug is added to the block copolymer and poly(ethylene glycol) composition the poorly water soluble drug is contained within the inner hydrophobic core. Accordingly, a pharmaceutical formulation containing the polymer composition of the present invention and a poorly water soluble drug can be stored as a stable liquid formulation without degradation of the biodegradable polymer block. The formulation is capable of solubilizing effectively a poorly water soluble drug in a body fluid or in an aqueous medium by forming a micelle, wherein the drug is entrapped in the core of the micelle.
In summary, the present invention is a combination of a block copolymer, as defined herein, suspended in a poly(ethylene glycol) medium which is a liquid. The amphiphilic block copolymer of the present invention comprises a hydrophilic poly(alkylene glycol) component and a hydrophobic biodegradable polymer component. When placed in an aqueous environment, such as body fluids or fomulated as a suspension, syrup or the like, the poly(ethylene glycol) medium facilitates the dispersion of the block copolymer which forms a polymeric micelle in the aqueous medium. When a poorly water soluble drug is added to the composition and placed in an aqueous environment, the drug is solubilized by incorporating the drug into the inner core of the micelle.
The polyalkylene glycol suitable for the hydrophilic component in the block copolymer of the present invention is a member selected from the group consisting of polyethylene glycol, monoalkoxy polyethylene glycol, or monoacyloxy polyethylene glycol wherein the molecular weight of the polyalkylene glycol is preferably within the range of 200xcx9c20,000 Daltons, and more preferably within the range of 1,000xcx9c15,000 Daltons. The content of the hydrophilic component is within the range of 40xcx9c80 wt %, preferably 40xcx9c70 wt %, based on the total weight of the block copolymer.
The hydrophobic biodegradable polymer component of the copolymer of the present invention is a member selected from the group consisting of polylactides, polycaprolactone, copolymers of lactide and glycolide, copolymers of lactide and caprolactone, copolymers of lactide and 1,4-dioxan-2-one, polyorthoesters, polyanhydrides, polyphosphazines, poly(amino acid)s and polycarbonates. Preferably, the hydrophobic biodegradable polymer component of the copolymer of the present invention is a member selected from the group consisting of polylactide, polycaprolactone, a copolymer of lactide and glycolide, a copolymer of lactide and caprolactone, and a copolymer of lactide and 1,4-dioxan-2-one. The molecular weight of the hydrophobic biodegradable polymer component is preferably within the range of 500xcx9c20,000 Daltons, and more preferably within the range of 1,000xcx9c10,000 Daltons.
The amphiphilic block copolymer of the present invention may be an AB type diblock, an ABA or BAB type triblock copolymer comprising a hydrophilic poly(alkylene glycol) A-block component (A) and a hydrophobic biodegradable polymer B-block component(B), which forms a micelle in an aqueous medium, and is dissolved or mixed homogeneously in a poly(ethylene glycol) medium.
The amphiphilic block copolymers can be prepared according to methods described in U.S. Pat. Nos. 5,683,723 and 5,702,717, hereby fully incorporated by reference. For example they may be prepared via ring opening bulk polymerization of one of the cyclic ester monomers, such as lactide, glycolide, or 1,4-dioxan-2-one with monomethoxy poly(ethylene glycol) (mPEG) or poly (ethylene glycol) (PEG) in the presence of stannous octoate as a catalyst at 80xcx9c130xc2x0 C. When the 1,4-dioxan-2-one is used as the monomer, the preferable reaction temperature is 80xcx9c110xc2x0 C. When a copolymer of 1,4-dioxan-2-one and lactide is used, the 1,4-dioxan-2-one monomer is first reacted with mPEG or PEG at 100xcx9c130xc2x0 C., the lactide monomer is then slowly added to increase the degree of polymerization of 1,4-dioxan-2-one. Since the conversion of 1,4-dioxan-2-one monomer is 50xcx9c60%, the added amount of this monomer should be more than the calculated amount when the two monomers, 1,4-dioxan-2-one and lactide, are added together. The block copolymer product is dissolved in dichloromethane or acetone, precipitated in diethyl ether, hexane, pentane, or heptane, followed by drying.
The poly(ethylene glycol) or its derivatives used as a dispersion medium for the composition of the present invention are water soluble polymers having high attraction for the hydrophilic component of the block copolymer. Preferably, the poly(ethylene glycol), or an appropriate derivative thereof, has a melting temperature of below about 70xc2x0 C., and a molecular weight of 200xcx9c10,000 Daltons. The poly(ethylene glycol), including derivatives thereof, can be represented as formula I:
Rxe2x80x94Oxe2x80x94CH2CH2xe2x80x94(O CH2CH2)nxe2x80x94Oxe2x80x94R xe2x80x83xe2x80x83[I]
wherein R is hydrogen, C1xcx9cC4 alkyl, benzyl, or acyl, and n is an integer of 3xcx9c220.
Examples of the C1xcx9cC4 alkyl in the formula I include methyl, ethyl, propyl, isopropyl, and butyl groups, and the acyl group includes formyl, acetyl, and benzoyl groups.
When preparing a pharmaceutical composition for IV or IM injection, a poly(ethylene glycol) having a molecular weight of 200 to 1,000 Daltons, and which can be dissolved within minutes in an aqueous medium, is preferred. When preparing a pharmaceutical composition for oral, ophthalmic, or external uses such as a patch or ointment, a poly(ethylene glycol) having a molecular weight of 1,000 to 10,000 Daltons and which can be dissolved slowly in an aqueous medium, is preferred. Any mixture of poly(ethylene glycols) having a weight average molecular weight within the above stated ranges may also be utilized.
The compositions of the present invention are especially useful for delivering poorly water soluble drugs having solubilities of less than 10 mg/mL. Examples of the hydrophobic drugs include anticancer agents, antiinflammatory agents, antifungal agents, antiemetics, antihypertensive agents, sex hormones, and steroids. Typical examples of the hydrophobic drugs are: anticancer agents such as paclitaxel, camptothecin, doxorubicin, daunomycin, cisplatin, 5-fluorouracil, mitomycin, methotrexate, and etoposide; antiinflammatory agents such as indomethacin, ibuprofen, ketoprofen, flubiprofen, diclofenac, piroxicam, tenoxicam, naproxen, aspirin, and acetaminophen; antifungal agents such as itraconazole, ketoconazole, and amphotericin; sex hormons such as testosterone, estrogen, progestone, and estradiol; steroids such as dexamethasone, prednisolone, and triamcinolone; antihypertensive agents such as captopril, ramipril, terazosin, minoxidil, and parazosin; antiemetics such as ondansetron and granisetron; antibiotics such as metronidazole, and fusidic acid; cyclosporine; and biphenyl dimethyl dicarboxylic acid.
An organic solvent, that is not an essential component in the composition of the present invention, may be added into the composition to facilitate better solubility of a drug and increase the loading efficiency into a micelle. The organic solvent employed in the composition is a polar solvent which is harmless to the body and miscible with water and poly(ethylene glycol). Examples of suitable organic solvents include ethanol, acetic acid, lactic acid, glycolic acid, N-methyl-2-pyrrolidone, benzyl alcohol, glycerin, N,N-dimethyl acetamide, propylene glycol, diethyl amine, and mixtures thereof.
The composition of the present invention may be prepared by dispersing the amphiphilic block copolymer into the poly(ethylene glycol) or its derivatives by one or more of the following methods. The composition may be first prepared without the presence of the drug or the composition may be prepared with the simultaneous incorporation of the drug.
Depending on the solubility of a hydrophobic drug in poly(ethylene glycol) or its derivatives, the composition containing a hydrophobic or a poorly water soluble drug is prepared by several methods as follows:
(1) Heating: When a poorly water soluble drug is soluble in poly(ethylene glycol), the drug and block copolymer are mixed with poly(ethylene glycol) and stirred at 30xcx9c100xc2x0 C. to form a solution. The solution is then cooled to room temperature and a homogeneous drug incorporated liquid composition is obtained.
(2) Adding an organic solvent: When a poorly water soluble drug is not readily soluble in poly(ethylene glycol), the drug and block copolymer are mixed with poly(ethylene glycol) and stirred while heating. An organic solvent is added into the mixture until the drug and the block copolymer are dissolved and form a clear solution. The solution is then cooled to room temperature and a homogeneous drug incorporated liquid composition is obtained.
(3) Solvent evaporation: When a poorly water soluble drug is practically insoluble in poly(ethylene glycol), the drug, block copolymer, and poly(ethylene glycol) are dissolved together in an organic solvent having a boiling temperature of less than 100xc2x0 C., such as ethanol, methanol, ethyl acetate, dichloromethane, chloroform, acetonitrile, or acetone. The organic solvent is then evaporated by heating and/or under vacuum, to yield a composition wherein the block copolymer incorporated with a drug is homogeneously dispersed in the poly(ethylene glycol).
The composition of the present invention, which is easily dispersed in an aqueous medium, is capable of solubilizing a poorly water soluble drug in water and can be formulated as: an oral formulation such as liquid and capsule; a transdermal formulation such as an ointment or patch; and an injection fluid for intravenous, intramuscular, or subcutaneous administration. When the composition is administered by injection, it can be dissolved in an appropriate medium for injection, eg. saline or DW5, prior to use, or can be injected without dissolution. For non-injection administration, eg. oral route, the composition is formulated with pharmaceutically acceptable additives, eg. mannitol, sorbitol, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose.
The composition of the present invention which, in an aqueous medium, forms a polymeric micelle, is especially suitable for the intravenous injection of a poorly water soluble anticancer agent such as paclitaxel.
The composition of the present invention can also be used as a carrier for any other poorly water soluble substances into the body as well as for poorly water soluble drugs.
While the following examples are provided for the purpose of illustrating certain aspects of the present invention, they are not to be construed as limiting the scope of the appended claims.